A portable device, such as a cellular telephone or a laptop computer, often is used with an external battery pack. In particular, such a battery pack includes one or more battery cells which are housed in a housing that is separate from the housing of the rest of the portable device. The use of a battery pack that has battery cells housed separately from the portable device facilitates the charging of the battery cells without tying up the portable device in the process, and it permits easy replacement of a battery pack, e.g., a discharged one, with another battery pack, e.g., a charged one.
A well known problem in the art of portable devices is that when a portable device is dropped its housing tends to fail. Typically the housing shatters, becomes deformed, or comes apart at its joints. So too, the housing of a battery pack which is for use with the portable device. Indeed, failure of the battery pack housing may occur when the battery pack alone is dropped or when the combination of a battery pack attached to a portable device is dropped. In addition, when the battery pack is attached to the portable device and the combination is dropped, there is a tendency for the battery pack to separate from the portable device.
The housing of a battery pack is often fashioned from two housing portions, one of which is usually mechanically weaker than the other. The two housing portions are joined at a joint which may or may not be as strong as the weaker housing portion of the battery pack housing. Such an architecture is employed for the battery pack because the battery pack is often a substantial portion of the overall portable device when coupled thereto. Therefore, to avoid the appearance of extra seams, one housing portion, typically the stronger one, forms all the visible housing of the battery pack. The other housing portion is typically smaller, weaker, and hidden, e.g., by being a recessed plate attached to the stronger housing portion. To reduce the weight of the battery pack, and thus the weight of the overall portable device, the smaller, weaker, hidden housing portion of the battery pack is often formed with holes through its surface, which tends to further weaken it.
When such a battery pack is dropped, typically, there is a sequence of multiple impacts. For example, the battery pack itself may strike the ground, possibly several times, and the battery cells themselves may strike the battery pack housing portions as well as each other, also possibly several times. The various strikes of the battery pack itself with the ground are collectively referred to as "clattering" while the various strikes of the battery cells within the housing are collectively termed "rattling". The net result of the clattering and rattling is that the battery cells can have an impact with the weaker housing portion at a velocity that is substantially higher than the velocity of the battery pack when it first strikes the ground. As a result, either the weaker housing portion can shatter or the stronger and weaker housing portions can become separated at the joint between them. Either of these results is typically a catastrophic failure that renders the battery pack unusable.